1. Field of the Invention
This invention relates generally to methods and apparatus for inflating tires, and more particularly, to methods and apparatus for selectively opening and closing access to a tire for inflation or deflation operations.
2. Description of the Related Art
The use of central tire inflation systems and tire maintenance systems are known. For example, over-the-road trucks, road tractors, and tractor trailers may be equipped with a tire inflation or maintenance system such as the Meritor® Tire Inflation System (MTIS) by Pressure Systems International (P.S.I.), the AIRGO® tire inflation system by AIRGO, Inc., the Cat's Eye® system by Link Manufacturing, Ltd., or a system provided by Dana Corp.
Such systems typically utilize pressurized air generated by a vehicle's compressor for use by the vehicle's braking system. The pressurized air is supplied to a rotating wheel hub by way of either a hollow axle or an air hose arranged in communication with the pressure source. A rotational coupling is arranged in communication with the wheel axle to transfer the supplied air to a tire mounted on a wheel that is attached to a hub rotationally mounted on the axle. An air hose extends from the rotational coupling to the tire's valve stem to facilitate the supply of air to the tire. A check valve is also arranged between the air source and the tire to facilitate pressurization of the tire while also preventing unintentional deflation thereof. A non-self relieving pressure regulator is typically used and arranged between the pressure source and the tire to control the supply pressure.
The check valves arranged along the air supply paths in these systems are one-way check valves, which allow air to flow into the tire but not from the tire. Typically, the check valves are Schrader valves, which generally provide low flow rates and impede rapid inflation of a tire. While these systems are known to increase tire inflation pressures when below a desired pressure, there are instances where the tire may become over inflated. For example, the tire pressure may be unintentionally over inflated or it may increase with increasing air temperature. Over inflation can be detrimental to tire and vehicle performance. For example, an over inflated tire may result in lower traction and increased wear. Over inflation may also increase tire stiffness, which may reduce vehicle ride comfort.
Therefore, there is a need to reduce a tire's internal air pressure to obtain a more desirable pressure. In the noted systems, however, the check valves prevent any flow of pressurized air from the tire's pressurization chamber. Accordingly, there is a need to better regulate a tire's internal pressure by providing a valve that not only allows an increase in tire pressure during vehicle operation, but also a decrease in tire pressure during vehicle operation.